1. Field of the Invention
The present invention relates to an image pickup apparatus capturing images of an object to be observed.
2. Description of the Related Art
Some methods are proposed that enable image pickup apparatuses, which capture images of an object to be observed by using an image sensor and display captured images on a monitor, to perform image capturing of a large image capturing area. Japanese translation of PCT international application No. 2008-510201 discloses an image pickup apparatus that divides a large image capturing area into plural small segmented areas which partially overlap each other, captures images of the plural segmented areas, and joins captured images (tile images) of the respective segmented area with each other to produce a whole image corresponding to the large image capturing area. Moreover, Japanese translation of PCT international application No. 2004-514920 discloses an image pickup apparatus that uses a line image sensor and performs image capturing with relatively moving an object to be observed and the line image sensor in one direction so as to perform scan image capturing for obtaining an image of the whole object.
In addition, Japanese patent Laid-Open Nos. 2009-003016 and 2009-063655 disclose image pickup apparatuses each of which performs plural image capturing operations by using an image sensor unit provided with plural image sensors two-dimensionally arranged, with relatively moving the image sensor unit and an object to be observed. Then, each apparatus disclosed therein combines captured images obtained through the plural image capturing operations to produce a combined image covering a large image capturing area including the whole object.
However, the image pickup apparatus disclosed in Japanese translation of PCT international application No. 2008-510201 sequentially performs a lot of the image capturing operations for a lot of the segmented areas one by one and then joins a lot of the captured images obtained through the respective image capturing operations with each other, which requires a long time to obtain the whole image. Moreover, the scan image capturing disclosed in Japanese translation of PCT international application No. 2004-514920 requires movement of the line image sensor from one end of the other end of the image capturing area and a somewhat long image capturing time in order to obtain good image quality, which takes a long time to obtain the whole image.
On the other hand, the image pickup apparatus disclosed in each of Japanese patent Laid-Open Nos. 2009-003016 and 2009-063655 obtains plural captured images by the respective image sensors in one image capturing operation and thus can obtain the whole image by several image capturing operations, which shortens a time required to obtain the whole image. However, in such an image pickup apparatus, an effective diameter of its optical system required to sufficiently introduce light from the object to the plural image sensors may be larger than that of a circle including the whole image capturing area. In other words, as compared with a case of covering the whole image capturing area by one image capturing operation, an optical system with a larger effective diameter may be needed in the case of using the two-dimensionally arranged image sensors.